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A cluster of zebra mussels sits on a navagation buoy that was pulled from Lake Superior by the USCG Cutter Alder. Park Service officials have confirmed the presence of zebra mussels on Isle Royale. Plans call for the complete eradication of the colony from the island's waters. File/Duluth News Tribune

Zebra mussels have invaded Isle Royale National Park, with Park Service officials Monday confirming the finding for the first time.

Park officials are concerned because Isle Royale holds one of the region's largest remaining populations of native mussels on small lakes on the island. Zebra mussels have in many cases wiped out native mussel populations across the Great Lakes.

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"A lot of the boats that come here come from harbors that have zebra mussel problems on other parts of [Lake Superior]," Isle Royale superintendent Phyllis Green said. "But we may never know exactly how they got here."

Green said her staff will do more than try to prevent the spread of mussels to inland waters. Green is calling for an all-out effort to eradicate the existing colony from the park's Lake Superior waters.

A colony of mussels was found at the west end of the island in Washington Harbor last week. A single zebra mussel also was found at the east end of the island.

Park Service officials say they believe the mussels are the smaller zebra mussels and not its larger cousin, the Quagga mussel, which is considered more menacing because it can reproduce in deeper, colder waters.

Isle Royale, Lake Superior's largest island, sits about 15 miles from Grand Portage off Minnesota's North Shore.

The finding comes 20 years after zebra mussels first were confirmed in Lake Superior in the Duluth-Superior harbor. Though the mussels can't move far on their own, they often are spread by boaters and anglers when the thumbnail-size critters hitchhike in bait buckets and on other gear or even in engine cooling lines and attached to hulls.

They also can hitchhike in the ballast water of larger ships, although ballasted ships aren't common in waters adjacent to Isle Royale.

Green said divers already have pulled 24 mussels off the Windigo dock. They haven't found any more but are continuing to search, she said.

Green said crews will continue to take water samples to check for zebra mussel larvae called veligers. She said it's unclear if the mussels were mature enough to reproduce. It's possible the Park Service could poison water near the dock to kill additional larvae.

Green made headlines in 2007 when she began treating ballast water in the park's Ranger III ferry boat that brings passengers and supplies to the island from the mainland -- the first boat to regularly treat ballast on the Great Lakes. So far, tests show the treatment has been working to kill any living organisms in the ballast tanks.

Doug Jensen, aquatic invasive species expert for Minnesota Sea Grant, said efforts to eliminate established populations of zebra mussels have generally been successful only in controlled areas, such as flooded mine pits. One eradication effort at New York's Lake George may show signs of success, he said.

"There haven't been many cases of actually eradicating an established population in a natural lake,'' Jensen said. "They'd have to be very localized to have any success. But maybe they caught it early enough.''